1. Field of the Invention
The invention relates to a process for detecting the operating state of a pump in a pump system, especially a centrifugal or positive displacement pump, with the following process steps: detection of at least one pressure and/or flow profile in the pump system, computation of at least one characteristic value from the pressure and/or flow profile, comparison of the computed characteristic value with at least one defined characteristic value or with a characteristic value range bordered by the characteristic value, the defined characteristic value or the characteristic value range bordered by it corresponding to the operating state of the pump of interest, and output of the operating state determined by the comparison, furthermore a process for detecting the operating state of a device with at least one hydraulic actuator, a sensor for executing the process, a sensor arrangement with a first sensor and with a second sensor and a diagnosis device for detecting the operating state of a pump in a pump system for transport of a liquid delivery medium.
2. Description of Related Art
Pumps are used in industry and research in innumerable and quite different applications, whether in large-scale process engineering systems or, for example, in small laboratory structures with only very small delivery amounts. Failure of a single pump is often associated with failure of the entire system, production shutdown and major costs.
The reasons for damage and failure of a pump are diverse; they are to some extent specific to the pump type used; although, there is a series of general causes which can lead both to adverse effects on centrifugal pumps and also to adverse effects on positive displacement pumps, especially causes which have to do with an unsuitable operating state and the resulting consequent damage to the pump.
One intake-side or low pressure-side cause of an undesirable operating state can be the entrainment of gas into the liquid delivery medium, with the result of the absence of lubrication of the pump parts which come into contact directly with the delivery medium and incipient wear due to the dry friction which then occurs, running hot of bearing ring seals and leaks which lead to backflows and reduced output. To detect gas entrainment, often, there is a sensor in the intake region of the pump for detecting the level in the delivery medium supply line, or the pressure on the outflow or pressure side of the pump is observed and a pressure drop below a minimum value is detected, and the reaction is the shutdown of the pump (see, e.g., German Utility Model DE 298 15 361 U1). The first process has the disadvantage that level measurement cannot detect or can only inadequately detect air bubbles distributed in the delivery medium and the associated gas entry, and conversely, the second process can only be used to detect comparatively large amounts of gas entry, and therefore, is not suited for many applications.
Another frequent problem in pump operation is formation of cavitation in the low pressure region of a pump in which gas bubbles can form within the delivery medium; this can be attributed to the fact that the local pressure within the delivery medium falls below the vapor pressure of the delivery medium. Sudden implosion of cavitations in regions of higher pressure of the delivery medium in the vicinity of pump parts can lead to their erosion as a result of very high, locally limited pulses which are applied, for example, to the impeller blades by the accelerated delivery medium. One known measure for preventing cavitation is to determine the pressure difference between the inflow and outflow side of a pump and to use it to recognize cavitation conditions with consideration of the pump rpm and theoretical delivery height (see, German Patent Application DE 198 58 946 A1). In these and similar processes, the disadvantage is that more and more measurement quantities must always be recorded with several sensors (intake-side and outflow side pressures of the pump, pump rpm) and in addition, special pump characteristics must often be known (for example, NPSH value, net positive suction head); this is associated with major costs.
German Patent Application DE 103 34 817 A1 discloses a process for fault detection in pumps in which the pump pressure is detected by measurement engineering and the pressure profile is subjected to frequency analysis. The amplitude of a single characteristic frequency of the pump is used as the characteristic value from the entire frequency analysis and is compared to a reference amplitude, comparison of the measured and defined amplitude allowing deduction of a fault. The disadvantage in this process is that the choice of only one value from the frequency spectrum of the pressure profile which has been detected by measurement engineering allows only limited information about the actual condition of the operating state of the pump, so that there are only limited possibilities for determination of the operating state of the pump.
German Patent DE 196 25 947 C1 discloses a process for early detection of problems in positive displacement pumps in which the pressure profile is detected by measurement engineering on the pressure side of the pump and the difference of pressure amplitudes in a certain frequency range is determined and used to detect a fault. Here, in turn, the disadvantage is also that, by choosing only a small region of the frequency spectrum which has been obtained from the pressure profile, only limited analysis possibilities of the operating state of the pump are available.